Optical devices for viewing magnified images of objects come in many forms, such as binoculars, telescopes and microscopes. Binocular telescope designs date back as far as the 1600's, but it was only with the invention of the modern prism binocular by Ignatio Porro in 1854 that binocular devices could begin to combine the desired features of high magnification, high resolution and compact size. Although numerous design developments have optimized aspects of these features, all have involved functional trade-offs whereby compact size can only be achieved by sacrificing high resolution, high magnification and ability to view objects in low light conditions.
These design constraints arise from the fact that the exit pupil diameter is ordinarily determined by the diameter of the objective lens unit divided by the magnification of the binoculars' optical viewing system. In order to keep the size of the binoculars compact, the objective lens unit must have a relatively small diameter but this, however, limits resolution and real magnification. Reduced levels of resolution and magnification are undesirable because the purpose of binoculars is to discern the details of distant objects by using high magnifications. Although it is possible to design a lens system with a small objective (e.g., 20 mm or less) and a high theoretical magnification (e.g., more than 10× power), the resulting system would have an exit pupil of less of than 2 mm which is acknowledged in the art as a design limitation for all optical instruments. An exit pupil size below 2 mm will have degraded performance due to diffraction, dimness and low contrast. Such systems are usually classified as having “empty” magnification because the viewer does not benefit from the higher magnification when it exceeds the resolving power of the human eye (which for purposes of this invention will be defined as 120 arc seconds). Accordingly, a compromise has been made between the size of the exit pupil and the amount of magnification provided to the user.
This design compromise is evident from a survey of commonly available binocular devices: at fixed magnifications of 10× power and above the smallest objective diameter is at least 21 mm and devices with higher magnification have objective diameters which are significantly larger. For example, the typical 12× magnification high resolution binocular has an objective diameter of at least 32 mm in order to achieve adequate resolution and low light viewing capability. Due to the larger diameters of the objectives of these devices, they are too large to be considered compact. As a comparison, a modern Bushnell® binocular model promoted as “compact” (the IMAGE VIEW™ Digital Imaging Binocular) is manufactured with only 8× magnification and a 21 mm objective.
Recently, efforts have been made to provide optical devices with digital image capture functionality, such as the IMAGE VIEW model mentioned above. These efforts combine an optical viewing system (e.g. binoculars) with a separate digital camera. This arrangement has certain limitations. Most importantly, although the device permits a digital image capture that relates to the image seen by the viewer in the optical viewing system, the design does not change what the viewer actually sees using the device and therefore does not improve in any way the binocular viewing experience. Moreover, because the digital camera has its own optical system, the resolving powers of the optical viewing system and the camera may be different. This difference in resolving power may result in the user electing not to record an image with the camera which the user would have recorded if he/she had seen the actual image the camera was recording.
Another approach that has been used to integrate digital imaging functionality with a binocular device is to record images received by the optical device on a sensor and then redisplay them on a single display which is then viewed by the user. One of the challenges with this approach is to integrate the optical system with the mechanical and electrical components so as to achieve pocketability. In addition, this existing approach alone does not achieve the high magnification and other viewing attributes of a high resolution, high magnification binocular.